Operation strategies for psychrophilic anaerobic digestion of swine manure slurry in sequencing batch reactors

The objective of this study was to evaluate the performance of psychrophilic anaerobic digestion in sequencing batch reactors (SBRs) under operating strategies that would optimize process performance and stability while minimizing the interference of the bioreactor operation with regular farm activities. Process performance was evaluated on (i) reduction in pollution potential; (ii) energy recovery; and (iii) odour reduction. Experiments were carried out in twelve 40-L SBRs. Experimental results indicated that psychrophilic anaerobic digestion of swine manure slurry at 20 degrees C in an intermittently fed SBR (i) reduced the pollution potential of swine manure slurry by removing 84-93% of the soluble chemical oxygen demand and 41-83% of total chemical oxygen demand; (ii) produced biogas at rates exceeding 0.48 L of CH4 per gram of volatile solids fed; and (iii) successfully reduced odours. Other findings were that (i) for all experimental runs, psychrophilic anaerobic digestion of swine manure slurry in SBRs was very stable; (ii) the process generally performed well without external mixing; and (iii) intermittent feeding of once or three times a week did not affect process stability and performance. As a result, this process requires little energy input and most of the energy produced will be available for farm use. Since this process is very stable, process feeding could be integrated with the routine operation of manure removal from the barn, thereby minimizing interference with other farm operations.